1. Field of the Invention
This invention relates, in general, to improved dielectric resonators wherein the spurious frequency modes are highly subsided.
2. Description of the Related Art
Microwave filters and dielectric resonator oscillators are widely used in the field of communication electronics especially in microwave telecom systems for Satellite telecom as well as terrestrial links and cellular/mobile handsets. Dielectric resonators (DRs) are key microwave passive components finding wide applications in miniature microwave filters and oscillators for generating resonating frequencies for communication. The resonance mode spectrum of a DR is so dense that the spurious (undesirable, HE11, HE12 or TM01δ,) modes may interfere with the dominant (desirable, usually TE01δ) mode. Thus it is valuable to attenuate the spurious modes for efficient transmission of the dominant (desirable) mode.
There have been several studies to improve the spurious free response of a DR configuration, while providing limited or no influence on the Q-factor for the DR.
The mode separation (in frequency) of the dominant (f0, desirable) and the nearest (the undesirable) mode has been found to be 0.58 f0 for a case of a ring DR shielded in a circular metal cavity. The comparative separation however tends to reduce for the DR in MIC configuration to (0.35 to 0.38)f0.
U.S. Pat. No. 4,706,052 describes a design of dielectric resonator with TE01δ mode being the primary mode used. The design is provided with a dielectric resonator having a plurality of dielectric resonator units which are combined into one unit by a connecting means, with a boundary being formed between adjacent dielectric resonator units. The dielectric resonator units are accommodated in a metallic conductive case with input and output members for electrical connection of said dielectric resonator with an external circuit. The design shifts a resonant frequency of spurious mode into a frequency zone higher than a resonant point by causing said spurious mode to pass through boundary surfaces or layers.
U.S. Pat. No. 5,059,929 provides a design of dielectric resonator which is constructed by piling a plurality of plate-shaped dielectrics one on the other under pressure or adhering respective dielectrics with an adhesive to each other so that faces thereof to which pressure is applied or faces thereof adhered to each other are parallel with an electric field in the dominant resonance mode of the dielectric resonator. The dielectric constant in the spaces to which pressure is applied or in the spaces in which the adhesive exists is low making it difficult for an electric field in a resonance mode other than a dominant resonance mode to pass through the spaces between the faces of the dielectrics to which pressure is applied or the faces thereof adhered to each. The spurious response is thus suppressed.
The disadvantages of the resonators of the said patents is that the mode separation changes with the change in the substrate thickness which does not provide versatility for choosing the substrate. Further, the mode separation degrades while tuning the device.
Thus there is still no dielectric resonator available in the art which efficiently generates the dominant desirable mode by subsiding the spurious modes. To fulfill this need, the present invention provides an improved dielectric resonator which overcomes all the above limitations.